1. Technical Field of the Invention
The present invention relates in general to the field of wireless packet-data communications, and in particular, by way of example but not limitation, to interoperability between mobile IP and RSVP during route optimization.
2. Description of Related Art
Mobile Internet Protocol (mobile IP) is a protocol designed to support mobile Internet access. Mobile IP permits continuous network connectivity anywhere within a network a mobile node happens to be located. Mobile IP is able to track a mobile node without having to change the mobile node's permanent IP address. In mobile IP, data is transmitted to the permanent IP address of the mobile node, which address is associated with a home agent of the mobile node. Most typically, when the mobile node is outside its home network, the home agent will forward data to the mobile node in care of a foreign agent through a process of encapsulating the data, most typically referred to as tunneling.
Once the data packets are received by the foreign agent, the data will be decapsulated and forwarded to the mobile node. Mobile IP includes mobile IP version 4 (mobile IPv4), specified in Internet Engineering Task Force (IETF) Request For Comment (RFC) 2002, and mobile IP version 6 (mobile IPv6). One of a number of differences between mobile IPv4 and mobile IPv6 is the absence of a foreign agent in mobile IPv6. In mobile IPv6, the mobile node handles some of the functions that the foreign agent handles in mobile IPv4, as will be described in more detail below.
The home agent is a node on the home network of the mobile node that tunnels packet data for delivery to the mobile node when the mobile node is outside the home network. The home network of the mobile node is a network that has the same network prefix of the permanent address of the mobile node. A foreign agent is a node on a foreign network that provides routing services to the mobile node while the mobile node is registered with the foreign agent. A foreign network is defined as any network other than the home network.
A mobile node that is outside its home network must register a care-of address with its home agent to receive terminating packet data from the home agent. The mobile node can register the care-of address through a foreign agent, which forwards mobile IP registration information of the mobile node to the home agent. A care-of address is the termination point of a tunnel for packet data forwarded to the mobile node when the mobile node is outside its home network. The mobile node registers its care-of address with its home agent so that packet data intended for the mobile node can reach the mobile node.
When the mobile node is in its home network, it can receive packet data from the home agent without using a care-of address. The care-of address of the mobile node can change when network conditions change, such as, for example, when the mobile node roams from a first foreign network to a second foreign network.
The roaming mobile node can potentially change its network attachment point each time it moves to a new IP sub-network, which roaming can potentially cause a disruption in delivery of packet data bound for the mobile node. Mobile IP permits changes in network attachments in a manner that ensures that packet data is seamlessly delivered across attachment points.
Reference is now made to FIG. 1, wherein there is shown a block diagram of a system 100 that illustrates mobile IP packet-data flow. The system 100 includes a mobile node 102, a foreign agent (FA) 104, a home agent (HA) 106, and a correspondent host (CH) 108. The home agent 106 is the home agent of the mobile node 102 and the foreign agent 104 is currently being accessed by the mobile node 102 for packet-data services. The correspondent host 108 is in communication with the mobile node 102 as described in more detail below.
The correspondent host 108 sends a packet intended for the mobile node 102 via a message 110 to the home agent 106. The home agent 106 delivers the packet from a home network of the mobile node 102 to a care-of address of the mobile node 102 via a message 112 to the foreign agent 104. The packet can be delivered from the home agent 106 to the foreign agent 104 via the message 112 only if the packet is tunneled in a manner that causes the care-of address of the mobile node 102 to appear as the destination IP address of the packet.
After the foreign agent 104 has received the packet, the foreign agent 104 decapsulates the packet, so that the packet will appear to have a home address of the mobile node 102 as its destination IP address. Because the now-decapsulated packet is addressed to the home address of the mobile node 102, the packet is processed properly by upper protocol layers, such as, for example, transmission control protocol (TCP). After the packet has been decapsulated by the foreign agent 104, the packet is sent to the mobile node 102 via a message 114. Mobile IP packet-data flow that follows a route similar to that of the messages 110, 112, and 114 is commonly referred to as triangle routing.
Packet data sent by the mobile node 102, such as, for example, in a message 116, is delivered according to standard IP routing procedures. Thus, a packet sent by the mobile node 102 to the correspondent host 108 would be sent via the message 116 and a message 118.
Reference is now made to FIG. 2, wherein there is shown a block diagram of a system 200 that illustrates discovery, registration, and tunneling of a care-of address of a mobile node. A care-of address discovery procedure used in mobile IP is based on the Internet Control Message Protocol (ICMP) Router Advertisement Standard as specified in Request for Comment (RFC) 1256. In mobile IPv4, router advertisements are extended to also include the care-of address. These extended router advertisements are known as agent advertisements. Home agents and foreign agents typically broadcast agent advertisements at regular intervals.
The system 200 includes the mobile node 102, the foreign agent 104, and the home agent 106. In a message 202, the mobile node 102 requests service from the foreign agent 104. In message 204, the foreign agent relays the request of the mobile node 102 to the home agent 106. In message 206, the home agent accepts or denies the request from the foreign agent in message 204. In message 208, the foreign agent 104 relays the acceptance or denial of the home agent 106 of the message 206 to the mobile node 102.
After the mobile node 102 obtains a care-of address from the foreign agent 104, it must inform the home agent 106 of the care-of address. In mobile IP, this is accomplished using the registration procedure illustrated in FIG. 2. The mobile node 102 sends a registration request, messages 202 and 204, using the User Datagram Protocol (UDP) with the care-of address information. This information is received by the home agent and, if the request is approved, the home agent 106 adds necessary information regarding the care-of address to its routing table and sends a registration reply (e.g., the messages 206 and 208) back to the mobile node 102.
All mobility agents (i.e., home agents and foreign agents) using mobile IPv4 must be able to use a default encapsulating mechanism included in the IP within IP protocol as defined by Request for Comment (RFC) 2003. The source of the tunnel (e.g., the home agent 106) inserts an IP tunnel header before the header of any original IP packet addressed to the home address of the mobile node 102. The destination of this tunnel is the care-of address of the mobile node 102. In IP within IP an indication that the next protocol header is also an IP header is accomplished by indicating in the tunnel header that a higher level protocol number is 4. The entire original IP header is thus preserved as the first part of the payload of the packet. Elimination of the tunnel header allows the original packet to be recovered.
Operation of mobile IP has been extended to permit more efficient routing procedures, so that IP packets can be routed from a correspondent host to a mobile node without being first routed to a home agent. These extensions are referred to as route optimization. In route optimization, a correspondent host receives a binding update message from a mobile node's home agent that includes the mobile node's care-of address. The binding update message specifies an association of the home address of the mobile node with a care-of address for that mobile node, along with a pre-determined remaining lifetime of the association. The binding is stored by the correspondent host in a binding cache and is used to tunnel IP packets by the correspondent host directly to the care-of address, thus bypassing the mobile node's home agent. Use of the binding update message eliminates the triangular routing illustrated in FIG. 1. IP packets sent by the correspondent host employ the triangle routing until the binding update message sent by the mobile node's home agent has been received by the correspondent host.
Route optimization also includes a binding request message. The binding request message is sent by the correspondent host to the home agent when the correspondent host determines that its binding should be initiated or refreshed. If the home agent cannot find or does not want to inform the correspondent host of the mobile node's care-of address, such as, for example, if the mobile node is in its home network, the home agent sends a binding update message to the correspondent host that includes a care-of address that is set equal to the mobile node's home address and an association lifetime set to zero. The correspondent host must then delete the binding cache entry for that particular mobile node upon expiration of the association lifetime.
Real-time packet-data services, such as, for example, IP multi-media and Voice over IP (VoIP), impose Quality of Service (QoS) requirements on networks that support these services. One way of meeting these QoS requirements is to reserve predefined resources on a packet-data session path used by the services. A Resource reSerVation Protocol (RSVP) has been specified in IETF RFC 2205 that can be initiated to provide necessary information to routers located in a packet-data session path used by real-time packet-data service applications.
RSVP can be used by an application to inform a serving Internet infrastructure of its Quality of Service (QoS) requirements. RSVP is initiated by an application at the beginning of a packet-data session identified by destination IP address, transport layer protocol type, and destination port number.
Resources reserved by RSVP for a given packet-data session are used for all packets included in that packet-data session. Therefore, all of the packets will include details of the session to which they belong. The primary RSVP messages are PATH and RESV messages. The PATH message, which is sent by an initiator of the packet-data session, explicitly binds the data path of the packet flow and describes the capabilities of the source. The RESV message, which is issued by the receiver of the initial packet data, follows exactly the same path that the PATH message took, hop-by-hop, back to the source. The RESV message may, on its way back to the source, install QoS states at each hop. These states are associated with the specific QoS resource requirements of the destination. The RSVP reservation states are temporary states (i.e., soft states) that must be updated periodically. If these states are not updated, they will be removed.
It is expected that real-time packet-data applications, such as, for example, VoIP or IP multi-media, will require a combination of either mobile IPv4 or mobile IPv6 and RSVP in order to ensure that the applications will not be terminated if the mobile node roams into another network and also to ensure that imposed QoS requirements will be satisfied. However, the route optimization, which applies to both mobile IPv4 and mobile IPv6, used to solve the triangle-routing situation discussed above causes inter-operability problems between mobile IP and RSVP.
There is accordingly a need for a method and system for inter-operability between mobile IP and RSVP during route optimization that solves these and other drawbacks associated with the prior art.